It is already known to prepare bisaryl methane compounds by the reaction of alkyl-substituted benzenes with paraformaldehyde in the presence of an acid catalyst such as sulfuric acid, C. M. Welch et al., J.A.C.S., 73, 4391 (1951). G. Casiraghi et al., Synthesis, 143 (1981) additionally disclosed a similar reaction between paraformaldehyde and phenols in the presence of an acid catalyst. It is also known that small amounts of bisaryl methanes are formed as by-products in the chloromethylation of aromatic compounds, L. I. Belen'kii et al., Russ. Chem. Rev., 46, 891 (1977).